Dietary and niche analyses of four endemic and sympatric batoid species of the subtropical South Atlantic Ocean

We aimed to characterize the trophic ecology and test the hypothesis of niche overlap between four sympatric batoid species of the subtropical South Atlantic. Data were collected between 2017 and 2022 from two artisanal fishery communities in southern Brazil. Batoid’s stomach contents were identified, separated into categories, and weighed. We calculated the Levins, Pianka’s, and Prey-specific index of relative dietary importance (PSIRI) and performed a similarity test using PERMANOVA and the similarity percentage (SIMPER) for niche analysis. We analyzed 229 stomachs of four batoid species, 187 containing foods. All species showed a narrow food niche. The most important diet items for each species were Leptochaela serratorbita and Onuphidae for Dasyatis hypostigma; Nematoda for Pseudobatos horkelii; L. serratorbita, Sicyonia dorsalis and Portunidae for Rioraja agassizii and Achelous spinicarpus and fish for Sympterygia bonapartii. The analyses showed dissimilarity among the species’ diets without significant niche overlap. Our results detected the absence of significant niche overlap among batoid species, suggesting other types of niche partitioning and spatiotemporal habitat variation. This information could be considered for local management plans.

Methods
Data were collected in two artisanal fisheries communities in coastal Southern Brazil (27° 22’ S, 48° 20’ W,) from July 2017 to March 2022. The biometric data (total length – TL, disc width – DW, weight, sex, stage of maturation) were recorded for all batoid individuals. Stomachs were removed, fixed in 10% formalin, and sorted in the laboratory. The content was identified to the lowest possible taxonomic level, quantified, and weighed for each batoid species. We used family identification as the lowest taxonomic level to compare diet between species (i.e., Fish, Portunidae, Varunidae, Onuphidae, Sicyonidae). Seaweed and substrate were considered as accidental ingestion and excluded from analysis (Aguiar & Valentin, 2010).